It was in the early spring of 1954, at the age of 19 and 6 years after entering the mountains. Inside I was a practitioner of Dao. But on the outside I looked like a wild beast wearing the mask of a man.

The next level of practice is Sam-hap danbup. In Gang-won-do's Chi-ak Mountains I devoted myself to the highest level of Dobup (Dao method). From that time, master Chung-woon would give me instructions and then leave. I think he was acknowledging my ability to practice by myself. He would return to observe the depth of my practice, give me more instructions, and then leave again. Sam-hap danbup is a stage that cannot be interpreted by theory. You would not believe even one out of a hundred if I were to tell you about it.
It is nothing but breathing through the pores of the skin, namely the pore breathing. This principle is called Sam-hap danbup. In the stage of Sam-hap (three union), three energies (heaven, earth, and man) are united. Sam-hap means the energy circulation through the whole body’s pores continues after a temporary stop of breathing through the nose and mouth. Could you be convinced? Probably not. It has been said that some types of lower classification creatures with no lungs or degenerated lungs can take in oxygen through their skin. But who can be convinced that a man could stop breathing with his lungs and breathe through his skin? But I have done this practice. A practitioner should not wear any type of clothing when practicing this. I did a year of ascetic practice with not even a piece of underwear on. You might feel some sympathy when you imagine me sitting on dead leaves under rocks in the deep mountains when it was storming and snowing. But I endured in the single heart of spreading Dao through my improvement.
My master said, "With every danbup you have earned from your practice until now, by preserving the energy of your whole body, you are in the stage of letting the won-gi of 天地heaven and earth in and out the pores of your skin after inhaling once. As you acquire practice, your haeng-gong develops freely. Constantly do your practice."
Master continued to appear suddenly and watch my practice progress and then would go again.
After a year and a half, in the fall of 1955, I gained self-confidence that I had almost accomplished pore breathing.
When pore breathing is mastered the principles of yin, yang, five-operations, and six-energies function freely in the human body. A practitioner can master the phenomenon of fire and water not approaching the body. This miracle is impossible without principle and practice. This Dao can only be, as you said, entered by practice and cannot be entered by theory. I can demonstrate this type of miracle anytime you want. I have demonstrated this many times throughout the country.